Project Summary/Abstract Obese adolescents and young adults (AYA) with type 2 diabetes (T2D) are significantly less active than non- diabetic peers, despite the many disease-related benefits of physical activity. Because in-person physical activity interventions for obese AYA are challenging to implement and have high attrition rates, there is an urgent need to engineer targeted physical activity interventions that are effective and scalable for obese AYA with prediabetes and T2D. Aligned with NIDDK priorities, the long-term objective of the proposed research is to develop an intervention that reduces the risk of disease progression in youth with prediabetes and T2D. The applicant will take full advantage of the rich scientific environment of the Children?s Hospital of Philadelphia and University of Pennsylvania to achieve her research and training goals, supported by an expert multidisciplinary mentorship and advisory team. This K23 will support the PI?s training in mixed methods research, behavioral economics, mHealth, physical activity interventions, and biobehavioral clinical trial design and analysis. The goal of the proposed research is to develop an effective mobile health (mHealth) intervention to increase moderate to vigorous physical activity (MVPA) in AYA with prediabetes or T2D, harnessing insights from behavioral economics and leveraging a highly efficient framework to determine effective intervention components. Aim 1 will determine attitudes, beliefs, and norms about, as well as barriers and facilitators to, engaging in daily MVPA by conducting semi-structured interviews of AYA with prediabetes or T2D. In Aim 2, theory-based and empirically-informed text messages to promote MVPA will be developed through adaptation of adherence- promoting text message banks developed by the PI?s mentors, using focus groups with patient stakeholders and insights from Aim 1. Aim 3 will determine intervention component settings that effectively increase MVPA and will consist of a 12-week factorial trial (Behavioral Economics for Activity Motivation) of 4 intervention components targeting theoretical mediators of MVPA: 1) text messages targeting Theory of Planned Behavior concepts of attitudes and norms, vs. simple reminders; 2) ramping-up vs. fixed step count goals, targeting perceived behavioral control; 3) financial incentives allocated up-front and lost for unmet goals vs. earned, targeting loss aversion; and 4) daily vs. weekly goals, targeting hyperbolic discounting (preference for smaller-sooner over larger-later rewards). The primary outcome is change in MVPA. Secondary outcomes include steps/day, proportion achieving 60 minutes MVPA/day, body mass index, hemoglobin A1c, and fasting insulin and lipids. The PI and mentors hypothesize that effective component settings will include text messages targeting attitudes/norms, ramped goal, loss-framed incentives and daily goals. Through this K23, the PI will be poised to compete successfully for R01-level funding to conduct a randomized controlled trial of the optimized intervention, helping to launch her career as an independent physician-scientist with expertise in health behavior change in AYA with prediabetes and T2D.